Conventionally, various inorganic and organic photoconductive substances have been known as a photoconductive substance in an electrophotographic photoreceptor. Since organic photoconductive substances, when being used as an electrophotograph, have advantages of having excellent transparency of the film, good film-forming ability and flexibility, and reduced cost, various substances have hitherto been suggested. In recent years, there is an increasing requirement that a photosensitive wavelength region of the conventionally suggested organic photoconductive substance extends to the wavelength of an infrared semiconductor laser to use the substance as a photoreceptor for digital recording such as for a laser printer. From this viewpoint, squaralilium compounds described in JP-A-49-105536 (the term "JP-A" as used herein means an unexamined published Japanese patent publication) and JP-A-58-21416, triphenylamine trisazo compounds described in JP-A-61-151659, phthalocyanine compounds described in JP-A-48-34189 and JP-A-57-148745 have been suggested as photoconductive materials for a semiconductor laser.
When organic photoconductive substances are used as a photoreceptor for a semiconductor laser, it is required first that they have a photosensitive region extending to a long wavelength and then that the photosensitive products formed have excellent sensitivity and durability.
In order to satisfy these requirements, intense investigation and development have been tried and particularly, with regard to phthalocyanine compounds, various reports about their crystal forms and electronically photographic characteristics have been made.
In general, it has been known that phthalocyanine compounds have several crystal forms depending on the difference of the treating processes and the differences of the crystal forms have a great influence upon the photoelectric transfer characteristics of the phthalocyanine compounds. As for the crystal forms of the phthalocyanine compounds, for example, concerning copper phthalocyanine, in addition to .beta. form which is a stable form, crystal forms such as .alpha., .epsilon., .pi., .chi., .rho., .gamma., and .delta. forms have been known. These crystal forms have been known to be able to cause mutual transition by mechanical deformation power, treatment with sulfuric acid, treatment with an organic solvent, thermal treatment, and other treatments (e.g., see U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989). As for non-metallic phthalocyanine, crystal forms such as .alpha., .beta., .gamma., and .chi. have been known.
Moreover, with regard to chlorogallium phthalocyanine, the crystal form of chlorogallium phthalocyanine having a diffractive peak at a specific Bragg angle has been described in Denshi Shasin Gakkai Shi, 26 (3), pp. 240 (1987), but it has a crystal form different from that of the invention, and there is no description of the application to an electrophotograph in this literature. On the other hand, JP-A-59-44053 and Shingaku Giho CPM 81-69, 39 (1981) report the application to an electrophotograph, and JP-A-1-221459 discloses a chlorogallium phthalocyanine having a diffractive peak at a specific Bragg's angle and an electrophotographic photoreceptor using the same.
However, the conventionally suggested phthalocyanines do not necessarily have a sufficient photosensitivity, and have problems in terms of dispersibility in a binding resin and stability of the dispersion, and are disadvantageous in that they tend to cause image defects such as fogging and black spots. For these reasons, further improvement has been desired.
The present invention has been done according to these requirements, and an object of the present invention is to solve the prior art's problems.
To be specific, the object of the present invention is to provide a process for producing a chlorogallium phthalocyanine crystal having a high sensitivity, excellent electrophotographic characteristics, and excellent dispersibility in a binding resin and stability of dispersion.